A flowmeter which is used extensively in hospitals for monitoring the flow rate of oxygen and other gases is incorporated in a fitting which is connectable to a gas supply line and which has an outlet to which a gas delivery line can be connected. The flowmeter, which is located in series with the inlet and outlet ports of the fitting, includes a vertically extending transparent tube which has a tapered bore, the bore size increasing with height of the tube, and a small ball or bobbin located within the bore of the tube. Gas which is delivered to the fitting flows upwardly through the tube and, in so doing, lifts the ball or bobbin to a height which is proportional to the flow rate of the gas. The tube is calibrated to provide a flow rate read-out (usually in liters per minute) for a given constant delivery pressure (usually 400 kPa) in accordance with the lift height of the ball or bobbin.
When used in an oxygen reticulation system, the flowmeter tube normally is located within an outer (transparent) tubular envelope, and the gas which travels up the tube passes into the outer envelope and down an annulus between the tube and the envelope to proceed toward the outlet of the fitting. Also, a valve element is incorporated in the fitting between the flowmeter and the outlet for regulating the flow rate of gas through and from the fitting.
The above described flowmeter has proved to be highly successful, at least in commercial terms, largely, so far as the inventor has been able to determine, because no acceptable alternative device has been developed. However, the flowmeter does have certain inherent deficiencies. The device must be orientated in a vertical direction when in use in order that it might provide an accurate read-out, and the upwardly projecting tube/envelope is vulnerable to breakage. Additionally, the flowmeter cannot be read from a distance and cannot conveniently be adapted to provide for remote monitoring or to provide an alarm in the event of unacceptably low flow rates.